In present IR image systems (IR cameras) focus on an object is manually controlled by turning a focus ring on an objective with an optical lens system for generating an IR image of an object. A mechanical mechanism translates the movement of the focus ring to a displacement of the lens system in the objective in order to adjust a focal point to centre on a focal plane of an image capturing device in the shape of an infrared sensor array in the camera.
As an alternative or as a complement to manual focus control, IR cameras are often provided with an electromechanical servo system for focus control. Such a focusing servo is usually controlled by a user via an electric switch or by an automatic focus control system. The focusing servo is in present IR cameras used either to actuate an electromechanical displacement mechanism for displacing a lens in relation to a fixed image capturing device or for displacing a movable image capturing device in the direction of the optical axis of a lens.
Servo controlled focusing, however, detaches the user from the direct and intuitive sense for focusing control rendered by manually controlled focusing mechanisms.